The present invention is directed to an improvement in a transport drive or indexing chain used in an indexing, vacuum-packaging machine. Examples of such conventional vacuum packaging machines with transport chains are disclosed in applicant's U.S. Pat. Nos. 4,951,444, 5,271,207 and 5,517,805, for example, which references are incorporated by reference herein. The invention has especial relevance to vacuum-packaging apparatuses, such as those manufactured by “TIROMAT”.
In a conventional, indexing vacuum-packaging machine, a lower or bottom film or film-web is indexed using an indexing advancing mechanism for situating the lower film at a forming station for forming transverse, multiple package-receptacles formed therein, and then to a sealing or sealing/vacuum station, where the upper film for completing the packages is applied, and vacuum-sealed. At each station, a lower tool is raised toward an upper, stationary tool for performing the requisite tasks at the respective station. The lower or bottom film, in which are formed a plurality of formed receptacles or packages, is indexed every cycle using an indexing or transport drive mechanism incorporating a pair of laterally-opposite, parallelly-arranged drive or indexing chains on either lateral side of the packaging machine. Each chain is made up of a series of pivotally-connected links or side plates, a series of bushings, a series of pivot rods mounted in the bushings which pivotally connect together the ends of the links or side plates, and a series of rollers also rotatably mounted by the series of the pivot pins, and a series of attachments each mounting a biased, retractable engaging pin-detent for engaging with perforations side-edges of the bottom film for translating the bottom film during every film cycle.
Hitherofore, all of the above-mentioned elements of each drive-chain have been made of nickel-plated carbon steel, and is typically a number 10 metric chain. The reason for this is in order to provide a strong, hard chain that wears very little over time. For example, if the pivot rods were to wear just 1/1000 inch, and assuming there are 1000 links along the length of the chain, then the chain will have stretched a total of one inch, which would cause misalignment of the film registration during the film-indexing cycles, which would thus necessitate continual re-alignment of the machine, which would thus cause downtime and loss of output.
There have been in the recent past numerous cases of bacterial infestation or contamination of food-processing and food-packaging machines and apparatuses, especially those associated with the listeria bacteria. It has been found the most common place where these bacterial infections start and grow is in the transport indexing chains. When such a machine or plant becomes infected with listeria, it is very difficult to clean, and causing large losses. In one attempt to solve this problem, entire chains, including all of the above-enumerated parts thereof, have been made of stainless steel, which is more resistant to listeria, or other bacterial, infection. However, since stainless steel is considerably inferior in overall wear in comparison to nickel-plated carbon steel, the above-mentioned wear of the pivot rods has occurred, along with the concomitant elongation of the indexing chain and concomitant misalignment or mis-registration of the bottom film at the various stations of the packaging machine.
The present invention has solved these interdependent problems by firstly noting that the locations along an indexing chain that are most likely to be receptive to bacterial infection are those areas that tend to rust, and, secondly, by noticing that those areas of the indexing chain that maintain adequate greasing or lubrication do not tend to rust.